1. Field of the Invention
The present invention relates generally to optical communication systems, and, more particularly, to an, optical communication system employing an optical waveguide with grating couplers disposed normal to the light sources and detectors.
2. Description of the Prior Art
Optical communication between circuits disposed parallel to each other has been described in which the optical light beam containing the data is in the form of a circularly polarized optical wave transmitted via free space, polarizers and beam splitting cubes. This optical link transmits the data from a source to an optical detector in the receiving circuit. Connectivity between the circuits requires collimation of the light for free-space propagation and thus must rely on line of sight for connectivity. Moreover, several optical elements are required including a one-quarter wave plate, a collimating lens, and a polarization beam splitting cube, all of which require precise optical alignment. Examples of the prior art are found in U.S. Pat. No. 5,204,866 and U.S. Pat. No. 5,113,403.
Various constructions of optical waveguides, including optical fibers, are provided with embedded gratings for either inserting light into or for removing light from the respective optical waveguide at an intermediate location or at different intermediate locations of the waveguide. For instance, U.S. Pat. No. 4,749,248 to Aberson, Jr., et al, discloses a device for tapping radiation from, or injecting radiation into, a single mode optical fiber. This patent discloses that it is possible to convert a guided mode in an optical fiber into a tunneling leaky mode or vice versa by forming a grating of appropriate periodicity at least in the core of the optical fiber, and either to remove the guided mode from the fiber core into the cladding by converting it into the leaky mode, and ultimately from the fiber altogether, or to insert light of an appropriate wavelength into the core to form a guided mode therein by directing light of a proper wavelength from the exterior of the fiber toward the grating to propagate in the fiber cladding and to be converted by the grating into the guided mode in the fiber core. The grating is formed in such a manner that fiber core regions of identical optical properties are situated in planes oriented normal to the longitudinal axis of the optical fiber. The ""248 patent, and also U.S. Pat. No. 5,042,897 to Meltz, et al, depicts the source being disposed at an acute angle to the waveguide so as to launch light longitudinally in one direction. Consequently, the source can only communicate to a selected node or nodes in the launched direction.
Also, dielectric waveguides comprising grating couplers have been developed for providing wavelength selective filters. One such application is in the distributed feedback (DFB) laser diode where the grating provides wavelength selective feedback to the laser cavity. When a second order grating is used in a DFB laser, the grating is capable of transmitting a portion of the light that is flowing through the waveguide normal to the surface of the dielectric waveguide, and thereby couple light out the top surface of the laser. This application of a grating coupler is able to couple light traveling in both directions within the dielectric waveguide to a free space beam that leaves the waveguide normal to the surface of the dielectric waveguide.
Today, an optical data bus architecture that generally employs a broadcast approach is desired. A broadcast approach is one that provides optical connectivity between any node on a data bus to all other nodes and its requirements are described in a military standard, namely MIL-STD-1773. MIL-STD-1773 establishes the criteria necessary for the optical data bus to be compatible with an electronic data bus and defines the required connectivity for an optical data bus and its protocol for addressing nodes within a system, but does not disclose a communication system.
What is needed, therefore, is an optical communication system that uses an optical waveguide with gratings disposed normal to the sources and detectors in the transmitting and receiving circuits, respectively, for carrying optical data bi-directionally through the waveguide such that the same data is provided simultaneously to multiple nodes in a broadcast manner.
The preceding and other shortcomings of the prior art are addressed and overcome by the present invention which provides a broadcast optical communication system. The system comprises an optical waveguide having a plurality of gratings. A grating is disposed at a first node and couples light impinging normally thereto into the waveguide, the coupled light propagates bi-directionally through the waveguide. A second grating emits a portion of the coupled light in a normal direction from the waveguide. An optical source is disposed proximate the first node for transmitting light normally to the first grating, and an optical detector is disposed proximate the second node for detecting the normally emitted light.
In another embodiment multiple optical waveguides and source-detector pairs are employed in a parallel data architecture to provide multiple channel broadcast communications.
The foregoing and additional features and advantages of this invention will become apparent from the detailed description and accompanying drawing figures below. In the figures and the written description, numerals indicate the various elements of the invention, like numerals referring to like elements throughout both the drawing figures and the written description.